The phenomenon known as “crab walking,” or sometimes “dog tracking,” describes a vehicle driving crookedly or diagonally even when the steering wheel is held straight. This is not a simple alignment issue but rather the symptom of a severe mechanical failure. It occurs when the vehicle’s front and rear axles are no longer tracking in parallel, resulting in the rear tires following a path offset from the front tires.
Structural Integrity Failure
Damage to the vehicle’s core structure—the frame, chassis, or unibody—is one of the most severe causes of crabbing. This structural damage usually originates from a significant impact event, such as a severe accident, rollover, or T-bone collision. The force of the impact can physically deform the high-strength steel that forms the vehicle’s foundation.
The deformation often manifests as a bend in the mounting points where the suspension components attach to the chassis. Even a slight twist or bend in the frame rail or strut tower can permanently offset the front axle relative to the rear axle. When the vehicle’s centerline is compromised, the thrust angle—the direction the rear wheels push the car—is permanently skewed.
This permanent structural offset means the vehicle is fundamentally misshapen, as the chassis no longer maintains the factory-specified geometrical relationship between the axles. Repairing this requires specialized frame alignment equipment, which uses laser measuring systems to diagnose the issue. Technicians must then use hydraulic pulling equipment to return the metal back to its original factory dimensions.
Rear Axle Assembly Misalignment
A cause distinct from overall frame damage is the failure or shifting of the entire rear axle assembly. This is common in vehicles with a solid rear axle, like many trucks and older SUVs, where the entire axle housing is one piece of metal. A heavy side impact, such as hitting a curb or another vehicle, can physically bend the solid axle housing tube itself.
Bending the axle housing compromises the settings for the rear wheels, forcing the entire assembly out of square with the front axle. This changes the camber and toe angle of both rear wheels simultaneously, causing the assembly to point slightly to one side. Since the two rear wheels are locked together on a single tube, they jointly contribute to the diagonal thrust, causing the vehicle to crab.
Modern cars and crossovers often use an independent rear suspension mounted on a rear subframe, which is a secondary frame bolted to the unibody. A severe lateral force or a significant pothole impact can shear or loosen the large mounting bolts connecting this subframe to the vehicle body. When the bolts fail to hold the subframe securely, the entire rear suspension system can shift laterally or rotate slightly.
This subframe shift causes the entire rear axle assembly to track at an incorrect angle relative to the front wheels. Even a minor rotation of the subframe’s mounting points creates a noticeable diagonal thrust angle. The driver must constantly apply an off-center steering input to counteract the rear assembly’s push.
Catastrophic Suspension Component Breakdown
The crabbing motion can also be triggered by the failure of specific, individual parts responsible for maintaining wheel alignment. This is less about a structural bend and more about a component breaking free or losing its connection. Key examples include control arms, also known as lateral links or trailing arms, which are designed to fix the wheel in its proper position relative to the chassis.
These suspension arms are engineered to manage the high tension and compression forces exerted during driving and braking. However, a sudden, sharp impact can exceed the component’s yield strength, causing the metal to snap or the mounting bolts to shear completely. Once a control arm breaks, the wheel is no longer constrained and can swing dramatically into an extreme toe-in or toe-out position.
This immediate, uncontrolled shift in a single wheel’s geometry creates an overwhelming side force that pushes the entire vehicle diagonally. Another common failure point involves the rubber bushings pressed into the ends of the control arms and links. These bushings isolate the suspension from the chassis, but if the rubber deteriorates or separates from the metal sleeve, it allows uncontrolled play.
This excessive play disrupts the intended suspension geometry under load, meaning the rear wheel’s toe angle changes dynamically. The resulting instability and shifting geometry cause the crabbing symptom.
Why Driving a Crabbing Car is Dangerous
A car exhibiting crab-walking behavior should be immediately taken out of service due to safety hazards. The primary mechanical danger is the rapid and uneven degradation of the tires. Since the rear wheels are constantly scrubbing sideways against the road surface, the tire tread is subjected to high friction.
This scrubbing action can destroy the tire tread quickly, leading to premature cord exposure and increasing the risk of a tire blowout. The driver is forced to maintain constant steering correction to keep the vehicle traveling straight. This constant off-center steering input leads to driver fatigue and slows reaction times.
The compromised handling geometry makes the vehicle unpredictable, particularly during emergency maneuvers. Stability control systems are designed to operate with factory-specified geometry, and severe misalignment can confuse these systems or render them ineffective. This instability increases the potential for a skid or loss of control, especially when braking hard or turning at highway speeds.